1. Field of the Invention
The present invention relates to telecommunications and, more particularly, to methods and systems for using a packet-based protocol, such as the Session Initiation Protocol (SIP), to provide communication services to mobile nodes, such as delivering short message service (SMS) messages to mobile nodes.
2. Description of Related Art
Text messaging has become a popular method of communicating using wireless telephones. The Short Message Service (SMS) protocol has been used to provide this text messaging capability. Relevant aspects of SMS are described in the IS-41 standards published by the Telecommunication Industry Association and in the GSM MAP standards published by the European Telecommunication Standards Institute. A recent revision of the IS-41 standards, titled “Cellular Radio telecommunications Intersystem Operations,” TIA/EIA/IS-41-D, published in 1997, is incorporated herein by reference.
Wireless telephones are also increasingly being used for packet-based communication. One approach for providing packet-based communication services to user equipment (UE) such as wireless telephones is based on a network architecture known as the Internet Protocol Multimedia Subsystem (IMS). The IMS approach is described in various documents that are published by the 3rd Generation Partnership Project 2 (3GPP2), including the following documents that are incorporated herein by reference:                “All-IP Core Network Multimedia Domain: IP Multimedia Subsystem—Stage 2,” 3GPP2 X.S0013-002-A, version 1.0, published November 2005;        “All-IP Core Network Multimedia Domain: IP Multimedia (IMS) Session Handling; IP Multimedia (IM) Call Model; Stage 2,” 3GPP2 X.S0013-003-A, version 1.0, published November 2005; and        “All-IP Core Network Multimedia Domain: IP Multimedia Call Control Protocol Based on SIP and SDP; Stage 3,” 3GPP2 X.S0013-004-A, version 1.0, published November 2005.As the third document suggests, the IMS approach (as currently envisioned) uses the Session Initiation Protocol (SIP) and the Session Description Protocol (SDP) to provide communication services to UEs. Relevant aspects of SIP are described in J. Rosenberg et al., “SIP: Session Initiation Protocol,” Request for Comments 3261, June 2002, which is incorporated herein by reference. Relevant aspects of SDP are described in M. Handley et al., “SDP: Session Description Protocol,” Request for Comments 4566, July 2006, which is incorporated herein by reference.        
Recently, an IMS approach for delivering SMS messages has been proposed. See 3rd Generation Partnership Project 2, “Short Message Service over IMS,” 3GPP2 X.P0048-0, version 0.7, published October 2006. In this proposal, a short message service gateway (SMS-GW) uses the SIP MESSAGE method to transmit SMS messages. The SIP MESSAGE method is described in B. Campbell et al., “Session Initiation Protocol (SIP) for Instant Messaging,” Request for Comments 3428, dated December 2002, which is incorporated herein by reference.